1. Field of the Invention
The present invention relates to a Stirling engine generating system having a Stirling engine in which solar heat is used as a heat source and a generator is driven by the Stirling engine.
2. Description of the Prior Art
In a Stirling engine in which solar heat is used as a heat input source for driving the engine, an output power of the engine varies in dependence on the radiation heat of the solar energy. In order to keep the engine efficiency at a high constant level, it is necessary to keep the temperature of the operational gas in the high temperature portion constant as high as possible.
A system which satisfies the above requirement is disclosed, for example, in U.S. Pat. No. 4,457,133. As shown in FIG. 4, in this system, a Stirling engine 20, for driving a generator 27, is operated by solar energy which is received through a radiation heat receiving hole 21. During this operation, the engine temperature at a high temperature portion is detected by a temperature sensor for 23 for estimating the temperature of an operational gas in the high temperature portion. Then, a temperature regulation device 26 calculates a predetermined value of the operational gas pressure in the engine in response to the estimated operational gas temperature and an operational gas pressure control device 22 regulates the operational gas pressure in the engine so as to let a difference .DELTA.P zero which is between the predetermined value and a detected value of an operational gas pressure sensor 25 at a difference device 24 (FIG. 6). Thereby, the engine efficiency is kept at a high level. As shown in FIG. 7, however, a wide regulation range of the operational gas pressure is required so that the high engine efficiency can be kept at a set level throughout the range within which the engine can generate a power in response to the change of the solar heat for ensuring the constant rotational speed of the engine. Therefore, in this system, an operational gas compressor 30 which is disposed in the operational gas pressure control device 22 is required as an essential component as shown in FIG. 5.
However, the above operational gas compressor, which generates a high pressure, has to be driven without lubrication so as not to pollute the clean operational gas. Therefore, the reliability and the durability of the system deteriorated.